A vehicle has parts that are subject to deterioration through long term use. The long term reliability of such parts can be forecast by testing a representative sample part on a test stand. The test stand is equipped with actuating devices that run movable portions of the sample part through a large number of repetitive cycles.
For example, a ball joint in a vehicle suspension is subject to deterioration through long term use. The ball joint includes a ball stud which is movable pivotally in a socket. A test stand for a ball joint has actuating devices that repeatedly pivot the ball stud back and forth in the socket. The repetitive cycles of back and forth movements are all the same.
A sample ball joint is tested by running it through a large number of repetitive cycles on the test stand. When the repetitive cycles have been completed, the resulting deterioration of the sample ball joint is measured. The long term reliability of the sample ball joint is thus defined in terms of its ability to withstand a number of cycles on a test stand. The long term reliability of identical ball joints is then forecast in terms of a number of cycles on a test stand.
A rack and pinion steering gear is another example of a vehicle part that is tested for long term reliability on a test stand. The steering gear has a steering rack which is connected at its opposite ends to a vehicle steering linkage. The steering gear further has an input shaft which is connected at its upper end to the vehicle steering wheel. The rack moves longitudinally in response to rotation of the input shaft.
A test stand for a rack and pinion steering gear has actuating devices that cooperate to rotate the input shaft back and forth in opposite directions, and simultaneously to move the rack longitudinally back and forth in opposite directions. A sample steering gear is tested by subjecting it to a large number of repetitive cycles of back and forth movements on the test stand. The long term reliability of identical steering gears is then forecast in terms of a number of cycles on a test stand.
Another type of test stand for a steering gear is equipped with actuating devices that control the ambient temperature and/or apply sprays of water or other environmental factors to simulate environmental conditions that can cause deterioration. A sample steering gear is tested by subjecting it to controlled environmental factors on the test stand. The long term reliability of identical steering gears is further defined and forecast in terms of those controlled factors.